The present invention relates generally to semiconductor structures, and more specifically, to semiconductor structures with crack stop structures.
As complementary-metal-oxide-semiconductor (CMOS) device scaling has been reduced in recent years, chip stacking methods are being explored as options for increasing system performance. Chip stacks can increase interconnect densities and reduce interconnect lengths and are usually formed with through silicon vias (TSVs) and fine pitch microbumps between chips. This requires integration of TSVs into chip design and process flows and can also increase difficulties of adequate cooling during operation.
Alternate methods of chip stacking have included providing wire bond chip-stacks, which have limited numbers of perimeter interconnects, and forming chip cubes using “T” connections where a transfer metal level is formed, the chips are joined together into a stack and the edges are polished. In one variant, a chemically inert transfer metal is used and other metals are removed from the polished edges by wet etching. In other variants, either the same metal is used or the chip metal levels are removed during wafer processing. The polished edge is subsequently processed to pattern an additional metal layer forming T connections to the transfer metal.
According to one embodiment of the present invention, a semiconductor structure is provided and includes a substrate having an edge surface and a device surface with a central area, a crack stop structure disposed on the device surface and a circuit structure including components disposed on the device surface in the central area and interconnects electrically coupled to the components. The interconnects are configured to extend from the central area to the edge surface while bridging over the crack stop structure.
According to another embodiment of the present invention, a semiconductor structure is provided and includes a substrate having an edge surface and a device surface with a central area and a peripheral section, a crack stop structure disposed on the device surface and including a continuous structure surrounding the central area and discrete structures at the peripheral section and a circuit structure including components disposed on the device surface in the central area and interconnects electrically coupled to the components. The interconnects are configured to extend from the central area to the edge surface while bridging over the crack stop structure.
According to yet another embodiment of the present invention, a chip stack including a plurality of stacked semiconductor structures is provided. Each semiconductor structure includes a substrate having top and bottom edge surfaces and a planar surface with a central area, a crack stop structure disposed on the planar surface and a circuit structure including components disposed on the device surface in the central area and interconnects electrically coupled to the components. The interconnects are configured to extend from the central area to the top and bottom edge surfaces while bridging over the crack stop structure.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects are described in detail herein and are considered a part of the claimed invention. For a better understanding, refer to the description and to the drawings.
The forgoing and other features, and advantages of the embodiments are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
In complementary-metal-oxide (CMOS) chips using low-k dielectric materials, a perimeter crack stop serves to prevent cracks from propagating from the dicing channel at interfaces between the low-k dielectric layers. The crack stop has typically been formed by two or more continuous rings of stacked metal around the perimeter of the chip with all metal lines and via layers up to and including a last metal layer incorporated.
When copper (Cu) is used as the wiring metallurgy in the chip back end of line (BEOL) wiring layers, it is often necessary to passivate the copper and protect it from oxidization. This can be accomplished by forming a conductive adhesion and barrier layer of tantalum (Ta) and tantalum nitride (TaN) on the bottom and sides of the copper lines and using a passivating dielectric cap layer above the lines. In a BEOL wiring design, finer pitch lines and low-k dielectric layers are used adjacent to the active Si devices to interconnect them. Subsequent upper layers are used for longer distance interconnections and are progressively thicker and have progressively larger minimum pitches. Also, in the upper wiring layers, oxide based dielectric layers may be used. The cracking concern is generally with the low-k dielectric layers and not the upper oxide based dielectric layers.
The low-k dielectric layers may consist of various materials along with capping layers. In a standard CMOS process flow, a final metallization layer may be included, which is formed of an aluminum (Al) alloy, with a barrier/adhesion layer and an antireflective layer. Aluminum is generally self-passivating and forms a limited, tough, adhering oxide when exposed to air. For some applications, this final aluminum is used to form wire bond pads around the perimeter of the chip.
In a typical chip, a crack stop is designed to prevent the propagation of a crack below a certain maximum length. A crack above this length could potentially have sufficient energy to rupture the crack stop. Generally, the critical length selected is significantly greater than the distance between the crack stop and the dicing channel, which are typically about 10-20 microns apart, so there is no possibility of the crack stop failing. In certain cases, the crack stop will be offset from the dicing channel by up to 200 microns, which could result in a crack that would potentially rupture the crack stop. Where the typical chip is to be assembled in a chip stack, after the chips are stacked together and bonded to form a “brick” containing multiple modules, the top and bottom edge surfaces are ground, polished and corner crossing connections are formed. Due to assembly tolerances, the location of the active devices and crack stops relative to the polished surface in the chips varies. To account for these variations, a grind/polish uncertainty region is needed and can range in width from about 20 to 200 microns.
Aspects of the present disclosure are directed to providing electrical connections across the crack stop, which do not compromise integrity or performance of the crack stop. Further aspects are directed to preventing or impeding the formation of cracks in the grind/polish uncertainty region. To that end, structures are provided that can accommodate these disparate requirements. That is, in the grind/polish uncertainty region, strengthening structures are provided between corner crossing wires and top layers are used to pass signals over the crack stop structures.
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The chip stack 10 further includes a circuit structure 40 for each of the semiconductor structures 11 (see
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As shown, the continuous structure 31 and the discrete structures 32 each include BEOL layers 300 of copper (Cu) material. The interconnects 42 are provided as corner crossing wires formed of a layer of metallic (e.g., Al or Cu) material. In the portions of the peripheral section 25 at the one or more sides of the central area 24 where the discrete structures 32 are formed, the discrete structures 32 act as strengthening structures between the interconnects 42. As noted above, the discrete structures 32 each include BEOL layers 300 of copper (Cu) material and are broken up into discontinuous islands.
In an exemplary application, a case of localized passivation failure after 4Di chip stack processing could result in oxidization of the copper (Cu) in the discrete structures 32 exposed by grinding and polishing. In such a case, segmentation of the discrete structures 32 and a lack of a continuous copper path between the grind/polish surfaces and the continuous structure 31 cooperatively eliminate a risk of damage to a portion of the discrete structures 32 and the continuous structure 31 by progressive oxidization. The discrete structures 32 also reduce a risk of shorting between the interconnects 42 if there are any defects in insulation layers between surfaces of the discrete structures 32 exposed by polishing.
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As mentioned above, when the BEOL layers 300 of copper (Cu) material are formed and passivated, the BEOL layers 300 take the shape of the continuous structure 31 and columns of the discrete structures 32 that are aligned between the locations where the interconnects 42 will be located. Similarly, when the vias 301 are formed, the vias 301 are formed between locations where the interconnects 42 are to be located. As such, with reference to
In accordance with alternative embodiments and, with reference to
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In accordance with further embodiments and, with reference to
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With the additional feature of being able to remove silicon areas from the design at a post wafer level test stage, many new applications are opened or available with regards to built-in-self-test (BIST) operations and/or any additional test and characterization functionality. Historically, BIST relates to circuitry placed inside of a chip area. However, with reference to
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the embodiments. The embodiments were chosen and described in order to best explain principles and practical application, and to enable others of ordinary skill in the art to understand the embodiments for various embodiments with various modifications as are suited to the particular use contemplated.
While the embodiments have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the embodiments first described.
The present application is a continuation of and claims the benefit of priority to U.S. application Ser. No. 13/553,559, which was filed on Jul. 19, 2012. The entire contents U.S. application Ser. No. 13/553,559 are incorporated herein by reference.
This invention was made with Government support under Contract No.: H98230-08-C-1496 awarded by the Maryland Project Office. The Government has certain rights in this invention.
Number | Date | Country | |
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Parent | 13553559 | Jul 2012 | US |
Child | 13565848 | US |